In a conventionally known structure of an engine, in accordance with a control map of an engine speed and a fuel injection amount, a controller calculates the fuel injection amount dependent on the engine speed, calculates an injection amount deviation as a fuel injection amount increase, and determines that the engine is in a transient state if the injection amount deviation exceeds a predetermined reference injection amount deviation. The structure is disclosed in Patent Literature 1 (PTL1).
According to such a conventional method for controlling an engine, an EGR valve in an EGR unit is fully closed if the controller determines that the engine is in a transient state as illustrated in FIG. 13, and response of the engine is thus secured while suppressing or reducing clogging of a DPF.